The present invention relates to a hydraulic control system of an automated manual transmission mounted on an automobile, and particularly relates to a technique effectively applied to an automated manual transmission having a plurality of change gear arrays.
A manual transmission (MT) for shifting gears by manual operation of a driver has an input shaft coupled with an engine and having a plurality of driving gears, and an output shaft coupled with driving wheels and having a plurality of driven gears respectively paired with the driving gears. A plurality of change gear arrays are provided between the input shaft and the output shaft. In such a MT, after a clutch is disconnected at the time of shift change, a pair of gears for transmitting power is switched selectively from the plurality of change gear arrays manually by use of a shift mechanism such as a synchro-mesh mechanism, and the clutch is then connected. Gear changing operation, that is, shift change is performed thus.
When the shift change and the clutch operation are carried out by a shift actuator which is operated by hydraulically, an automatic transmission based on the configuration of the manual transmission can be obtained. Such an automated manual transmission of this type (hereinafter referred to as “AMT”) having a plurality of change gear arrays has an advantage over a regular torque-converter type automatic transmission (AT) having planetary gears or the like in an automatic shift mechanism. That is, according to the automated manual transmission, the number of parts is reduced so that the weight can be reduced easily, and the transmission efficiency of the driving system is high.
For example, in such an AMT as disclosed in Japanese Patent Laid-Open No. 2000-55184, a starting clutch for shifting a crank shaft of an engine and an input shaft between a coupling mode and an uncoupling mode, that is, an input clutch is provided between the crank shaft and the input shaft, and a bypass clutch of a hydraulic multiple disc clutch type for transmitting torque from the input shaft to an output shaft at the time of shift change is provided for preventing shortage of shift torque from occurring.
The AMT disclosed in this publication adopts a fail safe in which the first speed gear stage is forcedly set by a return spring when an oil pump as an oil pressure source has a breakdown. According to the related-art fail safe, however, when electromagnetic valves are out of control due to a failure of an electric system during running of the vehicle in the fifth speed gear stage while the wet multiple disc clutch is coupled, the gear is shifted to the first speed gear stage forcedly. Due to the sudden speed reduction caused by this forced shifting, not only is the vehicle unstable, but there also arises a problem that the starting clutch put in a half clutch position is worn or burned.